(a) Field of the Invention
This invention relates to novel compounds classified in the field of organic chemistry as fluorans useful as color precursors, particularly in the art of carbonless duplicating, for example, pressure-sensitive and thermal marking systems; to 3,3-(substituted-diaryl)-5/6-carboxyphthalides useful as intermediates to the subject fluoran color precursors; to processes for preparing said fluorans and phthalides; and to pressure-sensitive duplicating systems and thermal marking systems.
(b) Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors for carbonless duplicating systems. Among the more important classes, there may be named phenothiazines, for example, benzoyl leuco methylene blue; phthalides, for example, crystal violet lactone; fluorans, for example, with which this invention is concerned, for example, 2'-anilino-6'-diethylaminofluoran and 2'-dibenzylamino-6'-diethylaminofluoran; and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289 which issued July 5, 1955, July 23, 1957 and June 26, 1962, respectively. Many of the color formers in the prior art suffer one or more disadvantages such as low tinctorial strength, poor light stability, low resistance to sublimation, low susceptibility to copiability of the color-developed form in standard copying machines, for example, a Xerox.RTM. copier, and low solubility in common organic solvents, the latter disadvantages thus requiring the use of specialized and expensive solvents in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copying systems.
The following items to date appear to constitute the most relevant prior art with regard to the instant invention.
U.S. Pat. No. 4,104,437, issued Aug. 1, 1978, discloses and claims a pressure-sensitive copy system bearing pressure-rupturable microcapsules containing a chromogenic compound having the formula ##STR1## and containing additionally in admixture a chromogenic precursor having the formula ##STR2## wherein R.sup.1 and R.sup.2 each represent an alkyl group; R.sup.3 and R.sup.4 each represent a hydrogen atom; a halogen atom, an alkyl group, a nitro group, an amino group, an acyl group, or a carboalkoxy group; R.sup.5 represents a hydrogen atom or an alkyl group, with the proviso that R.sup.5 represents an alkyl group only when R.sup.4 represents a hydrogen atom; R.sup.6 represents an alkyl group, an aryl group or an aralkyl group; and X and Y each represent a hydrogen atom, a halogen atom, a nitro group, a lower alkyl group, an aryl group, an alkoxy group, or a carboalkoxy group.
British Pat. No. 1,427,318, issued Mar. 10, 1976, discloses a fluoran having the formula ##STR3##
German Offenlegungschrift No. 2,242,005 which was published Mar. 15, 1973, discloses a process for the preparation of phthalides of the formula ##STR4## by interacting a 2-hydroxy or alkoxy-4-dialkylamino-2'-carboxybenzophenone with a phenol of the formula ##STR5## wherein R is hydrogen or alkyl and R.sub.2 is hydrogen, phenyl or phenyl substituted by alkyl in the presence of sulfuric acid at 10.degree.-30.degree. C. for 2-5 hours and then making alkaline to pH 8-10.5 to isolate the phthalide. Alternatively, by adjusting the pH to 10-11, heating the alkaline reaction mixture at 80.degree.-100.degree. C., the corresponding fluorans are formed. The compounds have disclosed utility as color formers for pressure-sensitive papers.